Electrodialysis apparatus having gaskets and membranes aligned to reduce leakage



May 9, 1967 M. s. MlNTZ ETAL ELECTRODIALYSIS APPARATUS HAVING GASKETS AND MEMBRANES ALIGNED TO REDUCE LEAKAGE 3 Sheets-Sheet 1 Filed June 6, 1962 FIG.4

I I// [/1 I I l/IIIII INVENTORS MILTON SHELDON MINTZ BY WILLIAM JOSEPH NELLEN ATTORNIEY M. s. MINTZ ETAL 3,318,795 ELECTRODIALYSIS- APPARATUS HAVING GASKETS AND MEMBRANES ALIGNED TO REDUCE LEAKAGE 1962 5 Sheets-Sheet g;

INVENTORS ATTORNEY MILTON SHELDON MINTZ BY WILLIAM JOSEPH NELLEN May 9, 1967 Filed June 6,

M. S. MINTZ ETAL ELECTRODIALYSIS APPARATUS HAVING GASKETS May 9, 1967 AND MEMBRANES ALIGNED TO REDUCE LEAKAGE 3 Sheets-Sheet 5 Filed June 6, 1962 INVENTORS MILTON SHELDON MINTZ BY WILLIAM JOSEPH NELLEN ATTORNEY 3,313,795 Patented May 9, 1967 Jersey Filed June 6, 1962, Ser. No. 200,509 4 Claims. (Cl. 204-301) This invention relates in general to fluid treatment devices and, more particularly, to electrodialysis stack construction.

An object of this invention is to provide a less costly, easily constructed, and easily maintained electrodialysis stack.

Another object of this invention is to provide an electrodialysis stack in which cross-leakage between adjacent fluid treatment cells may be greatly reduced or substantially eliminated.

A further object of this invention is to provide an electrodialysis stack having gaskets interspersed between ion selective membranes with the gaskets clamping at least the ends of the membranes and without the membranes or the gaskets requiring internal fluid flow manifold apertures.

Yet another object of this invention is to provide an electrodialysis stack construction in which gaskets may be fabricated easily by cutting off lengths of extruded stock.

A still further object of this invention is to provide integrally formed screen spacers and gaskets by filling only portions of a screen material to approximately the thickness of the screen material with a cold setting rubber compound or the like.

Many other objects, advantages and features of invention reside in the construction, arrangement and combination of parts involved in the embodiments of the invention and its practice as will be understood from the following description and accompanying drawing wherein:

FIGURE 1 is a perspective view of the outlet end of an electrodialysis stack according to this invention with two external flow ducts shown in position;

FIGURE 2 is a top view of a concentrating stream gasket;

FIGURE 3 is a top view of a dilute or product stream gasket;

FIGURE 4 is a section taken on line 4-4 of FIG- URE 2;

FIGURE 5 is a top view of a fragment of one end of an ion selective membrane used in the electrodialysis stack of this invention;

FIGURE 6 is a longitudinal vertical section through the electrodialysis stack of this invention with horizontal and vertical central portions broken away and with three collecting troughs shown in position;

FIGURE 7 is a top view of an anode washing stream gasket;

FIGURE 8 is a top view of a screen spacer according to a first embodiment of this invention;

FIGURE 9 is a top view of a combination screen spacer and gasket according to a second embodiment of this invention;

FIGURE 10 is a vertical section taken on line 10-10 of FIGURE 6;

FIGURE 11 is a vertical section taken on line 11--1I of FIGURE 6; and

FIGURE 12 is a top view of an enlarged fragment of a screen spacer according to this invention.

Referring to the drawing in detail, an elongated box 20 is built up by bolting a bottom plate 21 below two channel members 22 and 23 with bolts 24. A top plate 25 is then bolted above the channel members 22 and 23. When the top and bottom plates and the channel members are made of a conducting material such as aluminum or another metal, these members have their inward facing surfaces covered with a thin layer of an insulating material (not shown). Thin sheets of neoprene rubber may be glued with a suitable adhesive to the inward facing surfaces of the top and bottom plates 25 and 21 and the channel members 22 and 23 to serve as such an insulating material. This insulation is glued or otherwise fixed in place before the channel members and the top and bottom plates are bolted together to form the electrodialysis stack housing or box 20.

A single pass electrodialysis stack 26 may be preassembled and placed intact in the box 20 or the stack 26 may be assembled within the box 20. Thus the construction of this invention allows the replacement of a stack 26 as a unit within a box 20 should any of the elements of the stack 26 fail. This allows the storage of replacement stacks 26 which may be quickly installed in the boxes 20 of large scale and large capacity water purification installations or other fluid treatment systems.

As shown in FIGURES 6 and 11, upper and lower end blocks [27 and 28 are drawn toward each other by flat head screws or bolts 29 which pass downward through end block 27 and are screwed into tapered apertures in end block 28. Interspersed cation and anion permeable membranes 30C and 30A, for example, or other arrangements of ion selective material, extend between the blocks 27 and 28. As shown in FIGURE 5, the ends of these membranes 30A and 30C may contain apertures 31 formed at one end to accommodate bolts 29. Interspersed between the membranes 30C and 30A and also clamped between the end blocks 27 and 28 are the gaskets 32 and 33.

As shown in FIGURES 2 and 4, the concentrate stream gaskets 33 are flat rectangular plastic plates having two sets of grooves 34 formed in their upper surfaces. As shown in FIGURE 3, the dilute or product stream gaskets 32 may have larger sets of grooves 35 formed in their top surfaces. As shown in FIGURE 7, an anode washing stream gasket 36 is also formed from a rectangular plate and contains two centrally disposed sets of grooves 37. The gaskets 3-2 and 33 and the gasket 36 may contain apertures 38, 39 and 40, respectively, to accommodate bolts 29.

Referring now to FIGURES 6 and 11, gaskets 32 and 33 are alternately interspersed between membranes 30A and 30C. Beneath the lowermost gasket 33 and a membrane 30C is placed a gasket 36 which may have an inert or non-ion selective membrane 41 disposed under it.

Other means besides the bolts 29 may be used to clamp the end blocks 27 and 28 toward each other. In such a case the membranes 30A and 30C and the gaskets 32, 33 and 36 need not contain the apertures 31, 38, 39 and 40 to accommodate the passages of the bolts 29. If the apertures are not needed in the gaskets, the gaskets may be formed from plastic material extruded in long lengths with a cross section like that shown in FIGURE 4. These long lengths, each having a suitable cross section, may he very inexpensively and easily cut to the required lengths to form the gaskets. If bolts 29 are used as a clamping means, then the apertures 38, 39 and 40 may be punched or drilled in the gaskets.

Referring now to FIGURES 6, 8 and 10, screen spacers 42 are placed between the membranes 30A and 30C, beyond the gaskets 32 and 33. The screen spacers 42 are of substantially the same thickness as the gaskets 32 and 33 and may be formed from suitable expanded plastic material 43 as shown in FIGURE 12. The side edges 44 of the screen spacers are filled with material which forms a mechanical bond with the expanded mesh which holds the filling material within and to the screen material 43.

In one example of the formation of the screen spacers 42 according to this invention, an extruded mesh of 35 mils thick polypropylene screen, was slit to an eight inch width. Each lengthwise edge was then filled to one-half an inch width with a cold setting silicone rubber latex and the rubber was set. The rubber edges form resilient gasketing edges 44 which are integral with the screen 43. If the electrodialysis stack of this invention is used to purify water for human consumption, it is important that a rubber or other filler be used which has a catalyst and other ingredients of low toxicity.

As shown in FIGURE 6, the screen spacers 42 are laid to butt up against the edges of the gaskets 32 and 33.

Referring further to FIGURES 6 and 10, an anode 45 may be constructed to platinized titanium or platinum foil or wire which extends below a suitable screen spacer 46. One or more electrical leads 47 may lead from the anode 45 through the box 20. The volume of box below the membrane 41 is filled with a polyethylene foam material 48 behind the lower end block 28.

As may be further seen in FIGURES 6 and 10, above the uppermost membrane A behind end block 27 there is placed a sealed membrane bag 49 containing a cathode .50 which is of stainless steel screen material. An inlet tube 51 extends through channel member 22 and enters bag 49. A lead 52 also extends through channel member 22 to enter bag 49 and make an electrical contact with the cathode 50. An outlet tube 53 leads from the front of bag 49 through channel member 22. The outlet tube 53 may be seen in FIGURE 11. Another block of polyethylene foam 54 is placed above bag 49 to fill the volume of the box 20 above bag 49 in front of the end block 27. The foam blocks 48 and 54 may be made slightly thicker than the space they are to occupy so that, when the electrodialysis stack is assembled or placed within the box 20 and the top plate 25 is bolted to be pulled downwards, the bolting of top plate 25 will compress the foam blocks 48 and 54 and transmit the bolting force to the cells and hold the membranes and screen spacers Referring now to FIGURE 9, a second embodiment of this invention uses a screen spacer 55. The screen spacer 55 has its edges 56 of screen material 57 filled in the same manner described for the spacers 42. The forward end of the screen material 57 is also filled in two portions 58 and 59 leaving two unfilled portions 60 and 61. The unfilled portions 60 and 61 serve as passages to allow flow through the ends of the screen spacers 55 much as the channels 34 and allow flow through the gaskets 33 and 32. In assembling a stack with the spacers 55, alternate spacers 55 are inverted so that the passages leading from the alternate fluid treatment cells are vertically aligned. Apertures 62 may be formed through the end of the screen spacer 55 to accommodate the bolts 29. Thus the screen spacers 55 may be used in place of the gaskets 32 and 33 and the screen spacers 42.

Both embodiments of this invention may be used in the following manner. As shown in FIGURE 6, fluid to be treated is introduced through pipe 64 which extends through the end plate 65 which closes the rearmost end of the box 20. A space is left between the end plate 65 and the stack 26 so that fluid can enter the spaces between the membranes 30A and 30C and flow above electrode 45. This fluid flows along the central portions of the screen spacers 42 between adjacent pairs of membranes 30C and 30A. The leads 47 and 52 are connected to a suitable current source so that the cathode 50 and thet anode will function. Ions within the fluid treatment cells indicated by the letter D will pass through the membranes defining these cells D with the result that vent harmful precipitation at the cathode.

the cells D are diluting cells. Ions are retained in the cells marked with the letter C and additional ions pass into the cells C which act as concentrating cells. As fluid being treated moves through the fluid treatment cells D and C to the left as shown in FIGURE 6, fluid from the diluting cells D will reach the gaskets 32 to flow past them through the channels 35 and fluid from the concentrating cells C will reach the gaskets 33 to flow through the channels 34.

Referring now to FIGURE 11, fluid from the concentrating cells will flow from the grooves34 while fluid from the diluting cells will flow from the grooves 35. The grooves 35 are vertically aligned as a'rethe grooves 34. As shown in FIGURES 1, 6 and 11, a flow channel 70 is placed with its rearmost edge against the face of the stack 26 about the outer ends of each set of vertically aligned channels 35. A shorter flow channel 71 is similarly placed with its rearmost edge against the front face of the stack 26 about each set of vertically aligned channels 34. As shown in FIGURE 6, the longer flow channels or ducts 70 terminate over a trough 72 and the shorter flow channels or ducts 71 terminate over a trough 73. Thus the trough 72 collects flow from the diluting cells of stack 26 and the trough 73 collects flow from the concentrating cells C of the stack.

As may further be seen in FIGURE 6, fluid flows through the central portion of screen spacer 46 to wash the anode 45. This fluid flows from stack 26 through the channels 37 in the gasket 36. As shown in FIGURE 11, this electrode washing fluid falls directly downward to be caught in the central compartment 74 of the trough 75. A tube 76 drains this electrode washing stream from the central compartment 74.

Referring further to FIGURE 11, if a slight clearance 77 remains between the sides of stack 26 and the charinel members 22 and 23, leakage through the clearances 77 will fall downward to be collected in the outer portions 78 of the trough 75 and be drawn away through the tube 79. If it is desired to conserve fluid being treated, fluid from tube 79 may be recirculated to re-enter the inlet tube 64. If it is desired, a sufficient clearance 77, as shown in FIGURES l0 and 11, may be provided so that hydraulic resistance of fluid passing the length of the apparatus is less through the clearances 77 beyond the screen spacers and the membranes than it is within the fluid treatment cells C and D. In this case, any leakage past the sides 44 of the screen spacers 42 wil be from within the fluid treatment cells C and D into clearances 77. Therefore, in the construction of this apparatus, provision of a suitable clearance 77 may substantially reduce or completely eliminate any cross-leakage between adjacent fluid treatment cells C and D because any leakage from a given cell will only be outward,

The cathode 50 is hydraulically isolated from the rest of the stack 26 and it is washed by separate flow through the inlet and outlet tubes 51 and 53 because it is generally desirable to acidify the cathode washing stream to pre- Therefore, in many cases, the acidified cathode washing stream is recirculated. Furthermore, a higher flow rate may be required past the electrodes to carry with the electrode washing streams insoluble gases which might otherwise gather and bind the apparatus.

As shown in FIGURE 11, there are more grooves 35 leading from each diluting cell D than there are grooves 34 leading from each concentrating cell C. The number of grooves leading from a given fluid treatment cell determines the flow velocity within the cell. Therefore, as shown, a higher velocity is provided within the diluting cells to conserve the total amount of fluid required to be fed to the apparatus to produce a given amount of a dilute product. The rate of flow within the fluid treatment cells may also be regulated by otherwise varying the cross-sectional area of the channels leading from the cells, or the cell thickness or the spacer configuration,

A further advantage of this apparatus is that it allows immediate visual inspection of the operation of the stack. Any blockage within a fluid treatment cell will become apparent as the flow is reduced from a given set of channels 34 or 35. Also the functioning of a given cell may be checked by drawing samples from a particular set of channels 34 or 35 with a hypodermic needle for the like and then analyzing the samples.

In an example an electrodialysis stack comprising an aluminum box with detachable top, side, and bottom members was lined with neoprene rubber sheet and fitted with an assembly of nine cation selective membranes, nineanion selective membranes, eight dilute stream flow guide frames, nine concentrate stream flow guide frames, at platinized titanium anode and a stainless steel mesh cathode. The flow guide frames were 20 centimeters wide and 6 meters long. Flow channels in the dilute and concentrate flow guide frame were laterally displaced so that the effluent from these frames could be collected in separate troughs located adjacent the end of the stack. The following data was obtained during one trial run.

Feed, p.p.m. Na SO 1100 Product, ppm. 310 Cut (feed/product) 3.6:1 Dilute flow rate, cc./sec 58 Linear flow velocity, cm./ sec. 4. 6 Volts 25 Amperes 20.2 Current efficiency (dilute), percent 39 Feed pressure, grams/cm. 300

A membrane, as described herein, includes sheets, diaphragms, pellicles or other shapes or aggregates of material that have one very small dimension relative to the other two.

A flow guide frame or gasket as described herein is an element which can serve both to define the spacing between consecutive membranes in a fluid treatment device and to contain and direct the passage of fluid between membranes.

A fluid treatment area in a flow guide frame or membrane spacer as described herein is that area which is covered by a membrane surface and within which the fluid to be treated flows. In an electrodialysis device it is the area across which the predominant amount of current flows. In a dialysis device it is the area across which the predominant amount of material transfer takes place.

Flow channels within a flow guide frame are the conduits which connect the fluid treatment area in the flow guide frame either to a fluid source or to a fluid collection system. When the fluid collection system includes an atmospheric break, one end of the flow channels may be open to the air.

What is claimed is:

1. A fluid treatment device comprising, in combination,

(a) a rectangular container having an inlet and an outlet end,

(!b) substantially horizontal ion selective membranes disposed within said container defining fluid treatmerit cells between adjacent membranes, some of said fluid treatment cells producing a product stream,

(c) gaskets interspersed between and clamping the ends of said membranes at the outlet end of said container, said gaskets containing grooves forming passages conducting fluid from said fluid treatment cells past said gaskets, the passages conducting fluid from those fluid treatment cells producing a product stream vertically aligned in at least one set of passages laterally displaced from the other passages,

(d) screen spacers of substantially the thickness of said gaskets interspersed between said membranes within said container, said screen spacers butting against said gaskets, and,

(e) means disposed outside and hydraulically connected with said container beyond said gaskets collecting the product stream emerging from said gaskets from at least one set of said vertically aligned passages.

2. The combination according to claim 1 wherein said screen spacers have side edges which are filled with a plastic material, said fluid treatment cells being :between adjacent membranes and between the filled sides of said screen spacers.

3. An electrodialys-is stack comprising, in combination,

(a) a container having an inlet and an outlet end, said container having channel shaped side members and top and bottom plates bolted above and below said channel shaped side members,

(b) horizontally disposed alternate cation and anion selective membranes within said container defining concentrating and diluting cells between adjacent membranes,

(c) flat gaskets interspersed between and clamping the ends of said membranes at the outlet end of said container, said gaskets containing grooves forming passages conducting fluid from said concentrating and diluting cells past said gaskets, the passages conducting fluid from the concentrating cells being vertically aligned in at least one first set of passages, the passages conducting fluid from the diluting cells :being vertically aligned in at least one second set of passages laterally displaced from said at least one first set of passages,

(d) screen spacers of substantially the thickness of said gaskets interspersed between said membranes within said container, said screen spacers butt-ing against said gaskets, said screen spacers having side edges which are filled with a plastic material, said concentrating and diluting cells being between adjacent membranes and between the filled sides of said screen spacers,

(e) electrodes disposed above and below said membranes within said container, and

(f) collecting ducts having vertical walls placed against the outer edges of said gaskets on each side of each set of vertically aligned passages at the outlet end of said container, said ducts conducting flow from concentrating and diluting cells.

4. The combination according to claim 3 in which there is a slight clearance between the sides of said gaskets and the sides of said screen spacers and said channel shaped side members, the hydraulic resistance to fluid flow through said clearance being less than the hydraulic re sistance to fluid flow through the concentrating and diluting cells.

References Cited by the Examiner UNITED STATES PATENTS 2,758,083 8/1956 Van Hoek et al. 204-30l 2,784,158 5/1957 'Bodarner et al 204301 2,880,501 4/1959 Metz 204-301 2,881,124 4/1959 Tye 204-3 01 2,894,894 7/ 1959 Kressman 204-301 3,051,316 8/1962, MacNeil 204-301 FOREIGN PATENTS 852,272 10/ 1960 Great Britain.

JOHN H. MACK, Primary Examiner.

JOHN R. SPECK, Examiner.

G. E. BA'I'IIST, E. ZAGARELLA, Assistant Examiners. 

1. A FLUID TREATMENT DEVICE COMPRISING, IN COMBINATION, (A) A RECTANGULAR CONTAINER HAVING AN INLET AND AN OUTLET END, (B) SUBSTANTIALLY HORIZONTAL ION SELECTIVE MEMBRANES DISPOSED WITHIN SAID CONTAINER DEFINING FLUID TREATMENT CELLS BETWEEN ADJACENT MEMBRANES, SOME OF SAID FLUID TREATMENT CELLS PRODUCING A PRODUCT STREAM, (C) GASKETS INTESPERSED BETWEEN AND CLAMPING THE ENDS OF SAID MEMBRANES AT THE OUTLET END OF SAID CONTAINER, SAID GASKETS CONTAINING GROOVES FORMING PASSAGES CONDUCTING FLUID FROM SAID FLUID TREATMENT CELLS PAST SAID GASKETS, THE PASSAGES CONDUCTING FLUID FROM THOSE FLUID TREATMENT CELLS PRODUCING A PRODUCT STREAM VERTICALLY ALIGNED IN AT LEAST ONE SET OF PASSAGES LATERALLY DISPLACED FROMTHE OTHER PASSAGES, (D) SCREEN SPACERS OF SUBSTANTIALLY THE THICKNESS OF SAID GASKETS INTERPERSED BETWEEN SAID MEMBRANES WITHIN SAID CONTAINER, SAID SCREEN SPACERS BUTTING AGAINST SAID GASKETS, AND, (E) MEANS DISPOSED OUTSIDE ANBD HYDRAULICALLY CONNECTED WITH SAID CONTAINER BEYOND SAID GASKETS COLLECTING THE PRODUCT STREAM EMERGING FROM SAID GASKETS FROM AT LEAST ONE SET OF SAID VERTICALLY ALIGNED PASSAGES. 